Sensing the presence of a sheet of material or counting the number of sheets within a sheet-handling apparatus, such as a photocopier, can be a critical task. In most cases, the apparatus is designed to process one sheet of material at a time. The failure by the apparatus to feed a sheet on demand is, at the least, inefficient. Feeding more than the one sheet is similarly inefficient. But, more importantly, feeding more than one sheet can cause a sheet to become lodged or jammed within the apparatus stopping the operation of the apparatus and, possibly, damaging internal mechanisms within the apparatus.
Known sheet-sensing applications which demand a relatively high degree of accuracy and sensitivity can involve apparatuses which are complicated, bulky, sensitive to shock and vibration, and costly. For example, the use of optical transmission through a sheet(s) is complicated if the opacity of the sheet varies significantly or if the sheet is sensitive and vulnerable to the light being transmitted.
The use of dielectric measurement is similarly complicated when the dielectric property within a sheet varies significantly. And, dielectric sensors are known to be bulky.
The use of wide aperture analog photointerrupters, which include mechanically amplified lever arms, requires precise alignment and are susceptible to electro-optical changes over time. With mechanical amplification, this approach is also more susceptible to vibration and shock inherent within the apparatus.
Besides occasionally failing to feed a single sheet, known apparatuses are often plagued with inaccurate placement when feeding or transporting a single sheet. Commonly, sheets are introduced into a sheet-handling apparatus from a sheet container which is inserted into the sheet-handling apparatus. One known sheet pick-up mechanism involves the use of suction cups to grasp the top sheet in the container and guide that top sheet to another location within the apparatus. However, the accuracy of the pick-up mechanism can be adversely affected by, for example, vibration within the sheet-handling apparatus and can result in the misplacement or misalignment of the sheet. Misplacement and/or misalignment can result in a sheet being lodged or jammed within the sheet-handling process, or simply processed poorly.
As a result of the problems noted above, there is a need for a sheet-sensing apparatus which provides accuracy and sensitivity without the above-mentioned shortcomings. Another need includes the ability to count the number of sheets present with an apparatus. Another need includes the ability to properly position, align, and/or guide a sheet within a sheet-handling apparatus.